How should I structure a monthly budget when my expenses vary significantly from month to month?

How should I structure a monthly budget when my expenses vary significantly from month to month? I'm trying to build a monthly budget, but my expenses aren't consistent from one month to another. Some expenses are fixed, such as rent and subscriptions, while others vary significantly, such as groceries, transportation, entertainment, and occasional purchases. What is a good way to structure a budget in this situation? Should I base my budget on the average of the previous few months, use a fixed limit for each category, or keep a separate buffer for unexpected expenses? I'm particularly interested in a method that is simple enough to maintain every month without constantly adjusting dozens of categories. What approach has worked well for people with variable monthly spending?